The concept of multi-wafer parallel processing is expensive to fabricate considering the complexity of the design. And there is a limited market demand due to limited processing steps required for single wafer processing, resulting in a lack of return on investment (ROI) justification to pursue simultaneous multi-wafer cleaning. As such, no serious attempt has been made to create equipment for parallel processing of two or more wafers using a single cassette.
Now, because the shrinking geometries on processing chips require single wafer processing at several processing steps, the idea of multi-wafer processing with the efficiency of single wafer cleaning becomes relevant for future cleaning equipment technology. The current throughput issues are being addressed by increasing the fabrication floor space and the number of single wafer tools. Chamber stacking has also been done to reduce the tool footprint, but chambers are still isolated and throughput issues still exist.